Measurement of Impedance at Frequencies above 300 Mc (Correspondence)

I wonder if any of your readers can help me to find out whether the method described below has ever been proposed in the literature to measure the output impedance of signal sources in the frequency range above 300 Mc. Although it is realized that this method is in close relationship with Chipman's method, to the author's best knowledge it has not been proposed for the measurement of active two-terminal impedances, i.e., signal generator output impedances in particular.